Structural, dielectric, magnetic, optical, and electrical properties of double-perovskite Sr_1.5Mn_0.5Fe_0.5Hf_1.5O_{6< /sub> oxides}

Half-metallic ferromagnets (HMFs) exhibit semiconductor behavior for one spin projection and metal characteristics for the other, which have promising applications in spintronics. It is a great challengeable for HMFs to have wide spin energy gap, large saturation magnetization (M-S), and high Curie temperature (T-C) simultaneously. Here, we report the Sr1.5Mn0.5Fe0.5Hf1.5O6 (SMFHO) double perovskite compounds synthesized by solid-state reaction and display a magnetic T-C up to 804 K due to the strong Mn3+(up arrow)Fe3+(up arrow) spin interactions, which is the reported record in perovskite-type HMFs so far. The measured M-S value at 300 K was 4.87 mu(B)/f.u., and it further increased up to 6.09 mu(B)/f.u. at 2 K. The SMFHO powders exhibited butterfly-shaped magnetoresistance (MR)-H curve at 2 K, and the MR (2 K, 7 T) value was measured as -3.86% due to the intergranular magnetic tunneling effect. Variation of the resistivity of the SMFHO ceramics versus temperature exhibits a semiconductor behavior, and the electrical transport properties of the SMFHO ceramics are well studied by Mott's range jump model, thermally activated semiconductor conductance model and small polaron jumping model, respectively. The optical absorption spectrum of the SMFHO powders demonstrates an indirect optical bandgap of 3.56 eV. Our present work demonstrates the intriguing properties of the SMFHO oxides where high T-C, wide energy gap, and large M-S value are preserved at the same time, which open the way to their promising applications in advanced spintronic devices at or beyond room temperature.